New compound improves solar heat storage

In Spain, a solar power plant using molten salt to store heat recently produced power for 24 uninterrupted hours. But could there be an even better way to retain energy captured from the sun?

Scientists at MIT say there might be, pointing to their work with modified carbon nanotubes.

Finding a way to store the sun's energy as heat is something of a holy grail for researchers today, based on the theory that it can be retained longer and with less loss as heat than it can be if converted immediately to electricity.

The challenge in taking advantage of this better method of energy storage, the MIT team says, is that the materials used tend either to break down or require the use of ruthenium, an element they call "rare and expensive."

The MIT researchers say their big breakthrough in overcoming these challenges is in the use of modified carbon nanotubes, "tiny tubular structures of pure carbon, in combination with a compound called azobenzene," as the university described them.

"Not only is this new chemical system less expensive than the earlier ruthenium-containing compound, but it also is vastly more efficient at storing energy in a given amount of space — about 10,000 times higher in volumetric energy density."

Even better, this new system performs the remarkable feat of both grabbing solar radiation, and holding onto it.

"You've got a material that both converts and stores energy," says MIT associate professor Jeffrey Grossman, one of the study's co-authors.